We take advantage of the capability of the OTELO survey to obtain the H$alpha$ luminosity function (LF) at ${rm z}sim0.40$. Because of the deepest coverage of OTELO, we are able to determine the faint end of the LF, and thus better constrain the star formation rate and the number of galaxies at low luminosities. The AGN contribution to this LF is estimated as well. We make use of the multi-wavelength catalogue of objects in the field compiled by the OTELO survey, which is unique in terms of minimum flux and equivalent width. We also take advantage of the pseudo-spectra built for each source, which allow the identification of emission lines and the discrimination of different types of objects. The H$alpha$ luminosity function at $zsim0.40$ is obtained, which extends the current faint end by almost 1 dex, reaching minimal luminosities of $log_{10}L_{rm lim}=38.5$ erg s$^{-1}$ (or $sim0.002, text{M}_odottext{ yr}^{-1})$. The AGN contribution to the total H$alpha$ luminosity is estimated. We find that no AGN should be expected below a luminosity of $log_{10}L=38.6$ erg s$^{-1}$. From the sample of non-AGN (presumably, pure SFG) at $zsim0.40$ we estimated a star formation rate density of $rho_{rm SFR}=0.012pm0.005 {rm text{M}_{odot} yr^{-1} Mpc^{-3}}$.
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